65 research outputs found
Accurate Time-segmented Loss Model for SiC MOSFETs in Electro-thermal Multi-Rate Simulation
Compared with silicon (Si) power devices, Silicon carbide (SiC) devices have
the advantages of fast switching speed and low on-resistance. However, the
effects of non-ideal characteristics of SiC MOSFETs and stray parameters
(especially parasitic inductance) on switching losses need to be further
evaluated. In this paper, a transient loss model based on SiC MOSFET and SiC
Schottky barrier diode (SBD) switching pairs is proposed. The transient process
analysis is simplified by time segmentation of the transient process of power
switching devices. The electro-thermal simulation calculates the junction
temperature and updates the temperature-related parameters with the proposed
loss model and the thermal network model. A multi-rate data exchange strategy
is proposed to solve the problem of disparity in timescales between circuit
simulation and thermal network simulation. The CREE CMF20120D SiC MOSFET device
is used for the experimental verification. The experimental results verify the
accuracy of the model which provides guidance for the circuit design of SiC
MOSFETs. All the parameters of the loss model can be extracted from the
datasheet, which is practical in power electronics design
An Event-Based Synchronization Framework for Controller Hardware-in-the-loop Simulation of Electric Railway Power Electronics Systems
The Controller Hardware_in_the_loop (CHIL) simulation is gaining popularity
as a cost_effective, efficient, and reliable tool in the design and development
process of fast_growing electrified transportation power converters. However,
it is challenging to implement the conventional CHIL simulations on the railway
power converters with complex topologies and high switching frequencies due to
strict real_time constraints. Therefore, this paper proposes an event-based
synchronization CHIL (ES_CHIL) framework for high_fidelity simulation of these
electrified railway power converters. Different from conventional CHIL
simulations synchronized through the time axis, the ES_CHIL framework is
synchronized through the event axis. Therefore, it can ease the real_time
constraint and broaden the upper bound on the system size and switching
frequency. Besides, models and algorithms with higher accuracy, such as the
diode model with natural commutation processes, can be used in the ES-CHIL
framework. The proposed framework is validated for a 350 kW wireless power
transformer system containing 24 fully controlled devices and 36 diodes by
comparing it with Simulink and physical experiments. This research improves the
fidelity and application range of the power converters CHIL simulation. Thus,
it helps to accelerate the prototype design and performance evaluation process
for electrified railways and other applications with such complex converters
FPGA-Based Implicit-Explicit Real-time Simulation Solver for Railway Wireless Power Transfer with Nonlinear Magnetic Coupling Components
Railway Wireless Power Transfer (WPT) is a promising non-contact power supply
solution, but constructing prototypes for controller testing can be both costly
and unsafe. Real-time hardware-in-the-loop simulation is an effective and
secure testing tool, but simulating the dynamic charging process of railway WPT
systems is challenging due to the continuous changes in the nonlinear magnetic
coupling components. To address this challenge, we propose an FPGA-based
half-step implicit-explicit (IMEX) simulation solver. The proposed solver
adopts an IMEX algorithm to solve the piecewise linear and nonlinear parts of
the system separately, which enables FPGAs to solve nonlinear components while
achieving high numerical stability. Additionally, we divide a complete
integration step into two half-steps to reduce computational time delays. Our
proposed method offers a promising solution for the real-time simulation of
railway WPT systems. The novelty of our approach lies in the use of the IMEX
algorithm and the half-step integration method, which significantly improves
the accuracy and efficiency of the simulation. Our simulations and experiments
demonstrate the effectiveness and accuracy of the proposed solver, which
provides a new approach for simulating and optimizing railway WPT systems with
nonlinear magnetic coupling components
Rhodium(III)-Catalyzed C–H Alkenylation/Directing Group Migration for the Regio- and Stereoselective Synthesis of Tetrasubstituted Alkenes
An efficient Rh(III)-catalyzed C-H alkenylation/directing group migration cascade between indoles and alkynes for the assembly of tetrasubstituted alkenes is reported. The carbamoyl directing group migrates to the carbon of the alkene moiety of the products through rare Rh-catalyzed C-N bond cleavage after the C-H alkenylation step and thus acts as an internal amidation reagent. This protocol shows broad substrate scope, excellent regio/stereoselectivity, and good to excellent yields
Temperature-Controlled Divergent Synthesis of Tetrasubstituted Alkenes and Pyrrolo[1,2-a]indole Derivatives via Iridium Catalysis
We have achieved an Ir(III)-catalyzed temperature-controlled divergent synthesis of tetrasubstituted alkenes and pyrrolo[1,2-a]indole derivatives through C−H alkenylation/DG migration and [3+2] annulation, respectively. This method has various advantageous features: a) excellent regio- and stereoselectivity and good functional group tolerance, b) broad substrate scope and moderate to excellent yields, c) mild redox-neutral reaction conditions and operational simplicity
Chemo-, Regio-, and Stereoselective Assembly of Polysubstituted Furan-2(5H)-ones Enabled by Rh(III)-Catalyzed Domino C–H Alkenylation/Directing Group Migration/Lactonization: A Combined Experimental and Computational Study
Exploring multistep cascade reactions triggered by C–H activation are recognized as appealing, yet challenging. Herein, we disclose a Rh(III)-catalyzed domino C–H coupling of N-carbamoyl indoles and 4-hydroxy-2-alkynoates for the streamlined assembly of highly functionalized furan-2(5H)-ones in which the carbamoyl-directing group (DG) is given a dual role of an auxiliary group and a migrating acylating reagent via the cleavage of stable C–N bonds at room temperature. More importantly, the obtained furan-2(5H)-one skeleton could be further functionalized under air in situ via C5–H hydroxylation by simply switching the solvent or additive, providing fully substituted furan-2(5H)-ones with the installation of an alcohol-based C5 quaternary carbon center. Detailed experimental studies and density functional theory calculations reveal that a Rh(III)-mediated tandem C–H activation/alkyne insertion/DG migration/lactonization accounts for the developed transformation to achieve high functionalities with the observed exclusive selectivity. The potential biological application of the obtained furan-2(5H)-ones as a class of potent PPARγ ligands further highlights the synthetic utility of the developed methodology. This protocol is endowed with several salient features including efficient multistep cascade triggered by C–H activation, excellent chemo-, regio-, and stereoselectivity, high bond-forming efficiency (e.g., two C–C and two C–O bonds), solvent- or additive-controlled product selectivity, good functional-group compatibility, and mild redox-neutral conditions
Chemo- and Regioselective Synthesis of Functionalized 1H-imidazo[1,5-a]indol-3(2H)-ones via a Redox-Neutral Rhodium(III)-Catalyzed [4+1] Annulation between Indoles and Alkynes
Alkynes generally serve as C2 synthons in transition-metal-catalyzed C−H annulations, herein, exploiting electron-deficient alkynes as unconventional C1 synthons, the chemo- and regiospecific synthesis of functionalized 1H-imidazo[1,5-a]indol-3(2H)-ones via a redox-neutral rhodium(III)-catalyzed [4+1] annulation of N-carbamoyl indoles has been achieved. This process is characterized by high chemo- and regioselectivity, broad substrate scope, good tolerance of functional groups, moderate to high yields and mild redox-neutral conditions, thus affording a robust approach to access valuable 1H-imidazo[1,5-a]indol-3(2H)-ones
A review on the chemical constituents and pharmacological efficacies of Lindera aggregata (Sims) Kosterm
Lindera aggregata (Sims) Kosterm. (L. aggregata), which belongs to the genus Lindera in the family Lauraceae, is widely distributed in Asia and the temperate, tropical regions of North America. Its roots and leaves have been used for thousands of years as traditional Chinese medicine and/or functional food. To further explore its underlying nutritional value, this review provided a comprehensive insight into chemical constituents and pharmacological effects on L. aggregata. The phytochemical investigation of different parts of L. aggregata led to the identification of up to 349 components belonging to sesquiterpenoids, alkaloids, flavonoids, essential oils, and other compounds. Among them, sesquiterpenoids, flavonoids, and alkaloids are assessed as representative active ingredients of L. aggregata. A wide variety of pharmacological effects of L. aggregata, such as anti-hyperlipidemic, anti-tumor, anti-inflammatory, analgesic, and anti-oxidant, have been proved in vitro and in vivo. In summary, this review aims to provide a scientific basis and reference for further research and utilization of L. aggregata and lay the foundation for developing functional foods with potential active ingredients for the prevention and management of related diseases
Domain structure investigation of Mn-doped PIN-PMN-PT relaxor ferroelectric single crystals
sPLA2 IB induces human podocyte apoptosis via the M-type phospholipase A2 receptor
The M-type phospholipase A2 receptor (PLA2R) is expressed in podocytes in human glomeruli. Group IB secretory phospholipase A2 (sPLA2 IB), which is one of the ligands of the PLA2R, is more highly expressed in chronic renal failure patients than in controls. However, the roles of the PLA2R and sPLA2 IB in the pathogenesis of glomerular diseases are unknown. In the present study, we found that more podocyte apoptosis occurs in the kidneys of patients with higher PLA2R and serum sPLA2 IB levels. In vitro, we demonstrated that human podocyte cells expressed the PLA2R in the cell membrane. After binding with the PLA2R, sPLA2 IB induced podocyte apoptosis in a time- and concentration-dependent manner. sPLA2 IB-induced podocyte PLA2R upregulation was not only associated with increased ERK1/2 and cPLA2α phosphorylation but also displayed enhanced apoptosis. In contrast, PLA2R-silenced human podocytes displayed attenuated apoptosis. sPLA2 IB enhanced podocyte arachidonic acid (AA) content in a dose-dependent manner. These data indicate that sPLA2 IB has the potential to induce human podocyte apoptosis via binding to the PLA2R. The sPLA2 IB-PLA2R interaction stimulated podocyte apoptosis through activating ERK1/2 and cPLA2α and through increasing the podocyte AA content.</p
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